1. Field of the Invention
This invention relates to a continuous process for producing acrylonitrile butadiene styrene polymers, i.e., ABS polymers in solution in the presence of a radical initiator in at least two reaction zones while being stirred. Mercaptans are optionally used as chain transfer agents.
2. Description of the Prior Art
The following references relate to the state of the art as discussed below: (1) German Published Application No. 21 35 348, (2) German Published Application No. 24 48 596, (3) U.S. Pat. No. 3,903,199 and (4) U.S. Pat. No. 3,903,200.
Efforts to manufacture ABS polymers of polymodal particle structure, as mentioned in references (3) and (4), or of exclusively small particle diameters in the flexible phase are known. Reference (2) relates to the use of mineral oil to achieve small particle diameters in the flexible phase, however, the softening point of the polymers produced by this method is greatly reduced. Reference (2) also relates to a mass suspension polymerization for an ABS polymer used for the manufacture of mixtures with polyesters. An ABS component particle size of 0.5 micron to 2.0 microns is said to be achieved. Particles of less than 1 micron diameter are achieved by using high initiator concentrations (Example 1) and high reaction rates (page 8), however, this process cannot be used for continuous solution polymerization since the high reaction rates result in sticking of the material to the reactor upon higher throughput.
An object of this invention was to find a continuous process which results in small ABS polymer particles.